1. Field of the Invention
This invention relates to drive trains for vehicles, and specifically relates to clutch mechanisms for vehicles that utilize continuously variable transmissions.
2. Description of Related Art
Various recreational vehicles (e.g., motorcycles, scooters, go-karts, all-terrain vehicles (ATVs), snowmobiles, etc.) have drive trains that include continuously variable transmissions (CVTs) to transfer power from a propulsion unit (e.g., an internal combustion engine, electric motor, etc.) to a propelled device (e.g., a wheel(s), an endless track, etc.) to propel the vehicle. Such drive trains also typically include toothed gearing (e.g., additional reduction gears and/or a manually operated transmission) between the CVT and the propelled device.
In such drive trains, there is typically a constant driving connection between the propelled device of the vehicle, the gearbox, and the CVT, as well as possibly the engine. If the vehicle has to be pushed (e.g., if the engine is inoperable), rotation of the propelled device drives the belt of the CVT and the gears of the gearbox. The resistance of the gearbox and CVT to such rotation impairs the propelled device's ability to freely move, which makes it very difficult or even impossible to move the vehicle in difficult terrain, particularly if the vehicle itself is heavy.
In some vehicles, a centrifugal clutch is placed downstream on the drive train from the CVT (i.e., between the CVT and the propelled device). Consequently, the propelled device does not drive the CVT when the vehicle is being pushed. Unfortunately, such downstream centrifugal clutches are particularly difficult to design, manufacture, and install because they must operate at the low speeds and high torques that are present downstream from the CVT. Consequently, the centrifugal clutch must use very heavy fly-weights and an extremely rigid structure. The clutch must be very strong to endure the high torque that is present at both low and high speeds. The extreme operating conditions that the centrifugal clutch must endure produce fatigue and wear on the clutch, so that it is impossible to ensure long life and reliability. Finally, the addition of such a centrifugal clutch complicates assembly of the vehicle and makes the vehicle more expensive.